Here is the lowdown on Photostream (which i LOVE, btw) I have tested this and it all works.

When deleting photos on your iOS device…
* any photos taken BEFORE you upgraded to iOS 5.1 will be deleted on the DEVICE ONLY.
* any photos taken AFTER you upgraded to iOS 5.1 will be deleted EVERYWHERE (all iOS devices running iOS 5.1, AS WELL AS all Macs running the latest version of iPhoto or Aperture(*) – even if they have already been “downloaded” by iPhoto/Aperture)
* if your Macs are NOT running the latest iPhoto/Aperture(*), then I believe any deletions you do elsewhere will NOT be reflected on said Mac

(*)AN update to iPhoto came out recently (version 9.2.2); however no Aperture update that I am aware of has come out. Presumably Apple is working on one that will also work with Photo Stream deletions like the new iPhoto update does.

Also the “slide to open the camera” is a way to prevent the camera from accidentally launching if the phone gets poked (which has been known to happen). (in other words, they did it that way for the exact same reason that they did “slide to unlock” the way they did. )